Whole exome sequencing identifies a novel EMD mutation in a Chinese family with dilated cardiomyopathy

Abstract

Background: Variants in the emerin gene (EMD) were implicated in X-linked recessive Emery-Dreifuss muscular dystrophy (EDMD), characterized by early-onset contractures of tendons, progressive muscular weakness and cardiomyopathy. To date, 223 mutations have been reported in EMD gene and the majority of them caused a predominant skeletal muscular phenotype. In this study, we identified a novel deletion mutation in EMD exon 1, which results in almost a complete loss of emerin protein in a large Chinese family. However, the patients suffered severe dilated cardiomyopathy (DCM) but very mild skeletal muscle disorder.

Case presentation: Whole exome sequencing (WES) and linkage analysis were performed to identify the underlying mutation in a Chinese DCM family spanning five generations. A missense variation in the GPR50 gene was found co-segregated with the disease phenotype, whereas no functional alteration was detected in the variant GPR50 protein. When analyzing the failure sequences in the exome sequencing data, a novel deletion mutation (c.26_39delATACCGAGCTGACC) in EMD exon 1, was identified in this family. Different from the typical clinical features caused by most reported EMD mutations, patients in our study presented very mild skeletal muscle degeneration that had not been diagnosed until the mutation was found.

Conclusion: We described a family with rare clinical presentations caused by a novel EMD deletion mutation. Our findings broaden the heterogeneous spectrum of phenotypes attributed to EMD mutations and provide new insight to explain the genotype-phenotype correlations between EMD mutations and EDMD symptoms.

Figure 1

Haplotype analysis of family pedigree and ultrasonic cardiogram (UCG) study of proband A. (A) All sampled subjects in the pedigree are identified by their Roman numerals below the symbol. Arabic numerals denote each individual in a generation. Open symbols = unaffected; filled symbols = affected; symbols with a diagonal line = deceased subjects; squares = male; circles = female; arrows = the probands; Haplotype analysis is shown for chromosome X using 11 markers. The black bar indicates the haplotype assumed to carry the disease allele. The bars with black and white haplotypes indicate the existence of recombination event. The minimal in-linkage interval is 6.2 Mb of genomic DNA, 20.9 cM in size between DXS8091 and DXS1073 on chromosome Xq28. (B) Ultrasonic cardiogram study of proband A shows chamber enlargement. LA = left atrium; LV = left ventricle; RA = right atrium; RV = right ventricle.

Figure 2

Identification and functional study of the GPR50 variant. (A) Sanger sequence of codons 37-39 in exon 1 of GPR50 in a wild-type (WT) subject and proband B confirms the presence of the T38I variation. The variant nucleotide residue is indicated by a red rectangular. (B) The wild-type and variant GPR50 protein both located on the membrane of HEK293 cells. GFP-tagged GPR50 wild-type and variant plasmids were transfected into HEK293 cells. The red plasma membranes were labeled by Concanavalin A (Con A) and the nuclei were stained blue with DAPI. (C) The variant GPR50 protein did not alter the effect on melatonin-induced MT1 signaling. GPR50 wild-type and variant plasmids were transfected into MT1 stable transfection HEK293 cells, no difference of cAMP levels was deteced when treated with forskolin and melatonin, 48 h after trnasfection (ns, P > 0.05).

Figure 3

The proband B carrying a novel deletion mutation in EMD presented mild skeletal disorder. (A) Sanger sequence of codons 8-15 in exon 1 of EMD in a wild-type subject and proband B confirms the 14-bp deletion mutation (c.26_39delATACCGAGCTGACC). (B) A mild atrophy was observed in the proband B’s bicep and tricep muscles on the arm, no contraction had been detected in his elbows and Achilles tendons, and his calf muscles were surprisingly strong. (C) Hematoxylin-eosin staining of deltoid biopsy from proband B showed clear cross striation and normal myofilament fibers. Internally located nuclei and fiber splitting were found. Endomysial fibrosis and sarcoplasmic condensation were occasionally noted.